There have been increasing demands for a system for supporting high-speed data transmission in a mobile communication environment. In a mobile communication environment, each of terminals may be connected with a base station to transmit/receive high-speed data. So that the terminal is connected with the base station to transmit/receive data, the terminal and the base station may be required to be synchronized.
The terminal may be synchronized with the base station based on preamble signals transmitted from the base station. In general, a plurality of terminals may be connected with a single base station, and distances from the base station to each of the terminals may be different from each other. Accordingly, a propagation delay time for each terminal may be different from each other. The propagation delay time from the base station to the terminal may be not detected using only the preamble signals received from the base station.
In a communication system using an orthogonal frequency division multiple access (OFDMA) scheme, where a propagation delay time is greater than a predetermined time, interference between signals received from each of the terminals may occur. Accordingly, a receiving performance of the base station may be deteriorated, and thus high-speed data transmission may not be achieved.
Ranging signals may be used in order to synchronize the base station and the terminal in an uplink of a data transmission system. Each of the terminals may transmit the ranging signals to the base station, and the base station may measure the propagation delay time from the terminal to the base station, a frequency deviation, and the like, based on the ranging signals. The base station may synchronize the base station with the terminal based on the measured propagation delay time.
Where the terminal is initially connected with the base station or performs a handover to a new base station, a ranging process may be performed.
Where a plurality of terminals intends to simultaneously perform the ranging process with respect to a specific base station, the ranging signals transmitted by each of the plurality of terminals may collide with each other. In this case, the terminal may recognize the collision, and transmit new ranging signals.
Where a time required for performing the ranging process increases, an unnecessary load may be applied to the communication system, and a failure of the data transmission may occur. Accordingly, there is a need for a ranging scheme that may increase a ranging success rate and reduce a ranging process time.